Turn on turn off feedback drive switching circuit

ABSTRACT

A power transistor turns on and off in response to a switching signal applied to the base of a low level input transistor. Each of turn on and turn off transformers includes a primary winding having a relatively large number of turns, a main secondary winding having a number of turns N and N/2, respectively, and a feedback secondary winding having a number of turns such that the ratio of turns on main to feedback secondary windings is N and N/2, respectively.

United States Patent 15] 3,657,569 Froeschle 51 Apr. 18, 1972 [54] TURN ON TURN OFF FEEDBACK 3,161,837 12/1964 Lloyd .307/314 DRIVE SWITCHING CIRCUIT 3,482,118 2/1969 Mathamel; ..307/314 [72] Inventor: Thomas A. Froeschle, Framingham; Mass. PrimaUExaminer Donald D. Form, [73] Assignee: The Bose Corporation, Natick, Mass. Assistant Examiner-Harold A. Dixon [22] Filed Feb 19 1970 Attorney-Charles Hieken [2 1] Appl. No.: 12,747 [57] 1 ABSTRACT Related us, Application a A power transistor turns on and off in response to a switching [63] continuatiomimpan of N 6 520 Oct 2 signal applied to the base of a low level input transistor. Each 969 1 of turn on and turn off transformers includes a primary wind- U S 307/275 307/282 307/318 ing having a relatively large number of turns, a main s'econdag 1 331 ry winding having a number of turns N and M2, respectively, 51 1111.01. ..II03k 3/30 and a feedback semdafy winding havi'lg numb" 581 Field of Search ..307/275, 314, 288; 331/1 12 such that the ratio of main feedback Secondary windings is N and N/2, respectively. I 56] References Cited 15 Claims, 1 Drawing: Figure UNITED STATES PATENTS Sheehan ..33l/ll2 PATENTEBAFR 18 I972 3,657, 569

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INVENTOR THOMAS A" FROESCHLE BY MEM IQATTORNEYS TURN ON TURN OFF FEEDBACK DRIVE SWITCHING CIRCUIT REFERENCE TO COPENDING APPLICATION This application is a continuation-in-part of application Ser. No. 869,520 filed Oct. 27, 1969, entitled CURRENT CON- TROLLED TWO-STATE MODULATION BACKGROUND OF THE INVENTION The present invention relates in general to semiconductor device switching and more particularly concerns novel methods and means for turning a high power semiconductor switching device on and off rapidly and efficiently.

It is an important object of this invention to provide improved circuitry for turning a semiconductor switching device on and off. I

It is another object of the invention to achieve the preceding object with transformer drive.

It is another object of the invention to achieve the preceding objects with high power high speed switching transistors that are relatively low in cost. 1

It is still a further object of the invention to achieve one or more of the preceding objects with reliable circuitry that requires no adjustment and is relatively low in cost, bulk, weight and the total number of components.

SUMMARY OF THE INVENTION According to theinvention, there is an output semiconductor switching device having at least an output electrode, such as a transistor collector, and a control electrode, such as a transistor base. There are turn on and turn off transformer means each having primary winding means and main and feedback secondary means. The feedback secondary means are coupled in series with each other and the output electrode. Means including unilaterally conducting devices couple the main secondary winding in parallel to the control electrode so that the turn on and turn off secondary winding means may carry a current only when the dcvice is turning on, on, or turning off, respectively. Means are provided for selectively intercoupling the primary winding means in series with means including a unilaterally conducting device so that current flow through the turn on primary winding means initiates turn on of the output semiconductor switching device while blocking the current flowing through the turn off primary winding means of predetermined polarity causes the semiconductor switching device to turn off.

Numerous other features, objects and advantages of the invention will become apparent from the following specificationwhen read in connection with the accompanying drawing,

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of-which illustrates a schematic circuit diagramofanexemplary embodiment of the invention.

With reference now to the drawing there is shown a schematic circuit diagram of an exemplary embodiment of the invention. Output transistor Q2 turns on and off in response to a switching signal applied to input terminal 11 at the base oflow level input transistor 01. To this end there is a turn on transformer TI and a turn off transformer T2. Each transformer in cludes a primary winding, such as 12 and 13, having a relatively large number of turns, a main secondary winding, such as 14 and 15, having a number of turns N and M2, respectively, and a feedback secondary winding, such as 16 and 17, having a number of turns such that the ratio of turn on turns on the main secondary winding 14 to those on feedback winding 16 is N and the ratio of turn off turns on main secondary winding 15 to those on feedback winding 17 is N/2. Transformers T1 and T2 may also include reset windings l8 and 19, respectively, for resetting the core.

0 positely poled diodes D2 and D3 between An RC network 20 is in series with terminal 21 and primary winding 12. Diode D1 is poled as indicated and in series with primary winding 12 and NPN input transistor 01. The parallel combination of Zener diode 23 with the series combination of avalanching diode D4 and primary winding 13 shunt input transistor 01.

Feedback windings l6 and 17 are connected in series with positive terminal 21 and NPN output transistor Q2. Main secondary windings 14 and 15 are connected in series with opthe emitter and base of transistor Q2, the Zener diode 22 being in series with diode D3 and the base. Base resistor 22 is connected between the base and emitter of transistor Q2. A load (not shown) may be connected in series with the emitter or collector of transistor Q2.

Having described the circuit arrangement, its mode of operation will be described. To render transistor Q2 (or other suitable semiconductor switching device) conductive, input terminal 11 receives a signal that renders normally nonconductive transistor Q1 conductive. Transistor Q1 then draws current from low level power source terminal 21 through diode D1 and primary winding 12 of turn on transformer T1 to produce a relatively small current from secondary winding 14 that flows through diode D2 into the base of transistor O2 to render that transistor conductive. Transistor Q2 then draws collector current through secondary feedback winding 16 that regeneratively aids the current flowing through secondary winding 14 to rapidly saturate transistor Q2. The dots on windings l2, l4 and 16 designate the polarity relationship among the windings that achieves the result just described. The turns ratio N is very close to the beta of transistor Q2 with the collector saturated. For example, if a base current of one amp is the minimum required to maintain a saturated collector current of IO amps, N=l0.

Although transistor 02 also draws collector current through feedback secondary winding 17 of turn off transformer T2, the relative polarity of windings I5 and 17 and their turns ratio is such that the voltage developed across main secondary winding 15 is insufficient to render Zener diode Z2 conductive but is of polarity to forward bias diode D3 into conduction. This voltage is too small to cause Zener diode 22 to conduct because conducting transistor 01 effectively places a low impedance across primary winding 13 through forward-biased avalanching diode D4 that is stepped down to a lower potential across secondary winding 15.

To turn power transistor Q2 off, input terminal 11 receives a signal that renders transistor 01 nonconductive to divert the current formerly flowing through transistor Q1 through primary winding 13 of turn off transformer T2, Zener diode Z3 functioning to prevent transistor 01 from receiving too high an emitter-collector potential. The potential across primary winding 13 then rises sufficiently so that when stepped down across main secondary winding 15 of turn off transformer T2, the stepped down potential is high enough to overcome the Zener potential of Zener diode Z2 and forward-biased diode D3 so that base current is actually withdrawn from the base of transistor 02. Feedback secondary winding 17 of turn off transformer T2 is phased so that collector current flowing through winding 17 helps pull base current from transistor O2 to turn it off rapidly. After turn off, diode D4 may avalanche to protect itself from the sudden reversal in potential developed across primary winding 13 in response to transistor 02 cutting off.

When transistor O1 is cut off to reduce the flow of current through primary winding 12 of turn on. transformer T1, the polarity of the voltage developed across secondary winding 14 is such that diode D2 is reverse-biased after O2 is off.

Both the cores of transformers T1 and T2 are preferably reset on each cycle. Reset can be caused by providing the transformers with a constant reset current which flows through reset windings 18 and 19. The reset current causes the transfon'ner winding voltages to reverse after the ON TIME. The reverse voltages continue until the transformer cores are reset. Reset is completed when the reverse transformer windings voltesecond excitation equals the previous forward volt-second excitation.

Other reset techniques can also be used such as resonant reset and magnetizing current reset.

The circuit may be considered as having three modes defined by the conducting states of transistors Q1 and Q2. The first is the ON-ON mode with both transistors conducting and is limited by transistor Q2 reaching saturation. The second is the OF F-ON mode which occurs during turn off when transistor Q1 cuts off while transistor Q2 conducts and is limited in time to that required for transistor Q2 to cut off. The third is the OFF-OFF mode with both transistors not conducting.

The specific circuit described is by way of example only for illustrating the best mode contemplated for practicing the invention. Different types of transistors may be used, such as PNP transistors. The switched output device might be another device, such as a controlled rectifier having turn off gain. Certain refinements in the specific circuit may be omitted without departing from the principles of the invention.

Numerous uses and modifications of and departures from the specific embodiments described herein may now be practiced by those skilled in the art without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims.

What is claimed is:

1. Apparatus for turning a semiconductor switching means on and off comprising,

said semiconductor switching means having at least control and output electrodes,

first and second transformer means each having primary,

main secondary and feedback secondary winding means, an input terminal,

means responsive to a control signal on said input terminal for selectively drawing current through said first transformer means primary winding means to produce currents in said first transformer means main secondary winding means and both said feedback secondary winding means,

said feedback secondary winding means being in series with each other and said output electrode,

means responsive to the current production in said first transformer means secondary winding means for selectively establishing a current path between said first transformer means main secondary winding means and said control electrode to aid conduction of said semiconductor switching means,

said first transformer means primary winding means main secondary winding means and feedback secondary winding means, being poled in relationship to accelerate conduction in said semiconductor switching means,

means responsive to the control signal on said input terminal for selectively blocking current flow in both said primary winding means to initiate current flow in said second transformer main secondary winding means in response to current flowing in said second transformer feedback winding means to thereby tend to reduce the current flowing in said feedback secondary winding means,

means responsive to the current blocking in said second transformer means primary winding means for selectively establishing a current flow path between said second transformer means main secondary winding means and said control electrode,

said second transformer means primary winding means,

feedback and main secondary winding means relatively poled so that reduction in current through .said feedback secondary winding means is then accelerated.

2. Apparatus in accordance with claim 1 and further comprising reset winding means on each of said transformer means for resetting each of said transformer means at least once during a cycle embracing a turn on and turn off of said semiconductor switching means.

3. Apparatus in accordance with claim 1 wherein said means for selectively establishing a current path between said first transformer means main secondary winding means and said semiconductor switching means control electrode comprises a first unilaterally conducting device intercoupling the latter winding means and said control electrode.

4. Apparatus in accordance with claim 3 wherein said means for selectively establishing a current path between said second transforming means main secondary winding means and said control electrode comprises a second unilaterally conducting device.

5. Apparatus in accordance with claim 4 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and said control electrode.

6. Apparatus in accordance with claim 1 wherein said means for selectively establishing a current path between said second transformer means main secondary winding means and said control electrode comprises a second unilaterally conducting device. I

7. Apparatus in accordance with claim 6 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and said control electrode.

8. Apparatus in accordance with claim 1 wherein said means for selectively drawing current through said first transformer means primary winding means comprises a second semiconductor switching means having at least a control electrode coupled to said input terminal and coupled to the latter winding means by a first primary unilaterally conducting device.

9. Apparatus in accordance with claim 8 wherein said means for selectively interrupting current flow comprises said' second semiconductor switching means and a second primary unilaterally conducting means intercoupling the latter device and said second transformer means primary winding.

10. Apparatus in accordance with claim 9 and further comprising a primary Zener diode connected across said second semiconductor switching means for limiting the voltage developed thereacross.

11. Apparatus in accordance with claim 9 wherein said means for selectively establishing a current path between said first transformer means main secondary winding means and said first semiconductor switching means control electrode comprises a first unilaterally conducting device intercoupling the latter winding means and the latter control electrode.

12. Apparatus in accordance with claim 11 wherein said means for selectively establishing a current path between said second transforming means main secondary winding means and said first semiconductor switching means control electrode comprises a second unilaterally conducting device.

13. Apparatus in accordance with claim 12 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and the latter control electrode.

14. Apparatus in accordance with claim 13 and further comprising a primary Zener diode connected across said second semiconductor switching means for limiting the voltage developed thereacross.

15. Apparatus for turning a semiconductor switching means on and off comprising,

said semiconductor switching means having at least control and output electrodes,

at least turn-on, turn-off and feedback winding means,

an input terminal,

means responsive to a control signal on said input terminal for producing currents in said turn-on and feedback winding means,

lOl032 OSll said feedback winding means being in series with said semiconductor switching means output electrode,

means responsive to the current production in said turn-on winding means for establishing a current path between said turn-on winding means and said control electrode to aid conduction of said semiconductor switching means,

said turn-on and feedback winding means being poled in relationship to accelerate conduction in said semiconductor switching means,

means responsive to the control signal on said input ter- 

1. Apparatus for turning a semiconductor switching means on and off comprising, said semiconductor switching means having at least control and output electrodes, first and second transformer means each having primary, main secondary and feedback secondary winding means, an input terminal, means responsive to a control signal on said input terminal for selectively drawing current through said first transformer means primary winding means to produce currents in said first transformer means main secondary winding means and both said feedback secondary winding means, said feedback secondary winding means being in series with each other and said output electrode, means responsive to the current production in said first transformer means secondary winding means for selectively establishing a current path between said first transformer means main secondary winding means and said control electrode to aid conduction of said semiconductor switching means, said first transformer means primary winding means main secondary winding means and feedback secondary winding means, being poled in relationship to accelerate conduction in said semiconductor switching means, means responsive to the control signal on said input terminal for selectively blocking current flow in both said primary winding means to initiate current flow in said second transformer main secondary winding means in response to current flowing in said second transformer feedback windIng means to thereby tend to reduce the current flowing in said feedback secondary winding means, means responsive to the current blocking in said second transformer means primary winding means for selectively establishing a current flow path between said second transformer means main secondary winding means and said control electrode, said second transformer means primary winding means, feedback and main secondary winding means relatively poled so that reduction in current through said feedback secondary winding means is then accelerated.
 2. Apparatus in accordance with claim 1 and further comprising reset winding means on each of said transformer means for resetting each of said transformer means at least once during a cycle embracing a turn on and turn off of said semiconductor switching means.
 3. Apparatus in accordance with claim 1 wherein said means for selectively establishing a current path between said first transformer means main secondary winding means and said semiconductor switching means control electrode comprises a first unilaterally conducting device intercoupling the latter winding means and said control electrode.
 4. Apparatus in accordance with claim 3 wherein said means for selectively establishing a current path between said second transforming means main secondary winding means and said control electrode comprises a second unilaterally conducting device.
 5. Apparatus in accordance with claim 4 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and said control electrode.
 6. Apparatus in accordance with claim 1 wherein said means for selectively establishing a current path between said second transformer means main secondary winding means and said control electrode comprises a second unilaterally conducting device.
 7. Apparatus in accordance with claim 6 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and said control electrode.
 8. Apparatus in accordance with claim 1 wherein said means for selectively drawing current through said first transformer means primary winding means comprises a second semiconductor switching means having at least a control electrode coupled to said input terminal and coupled to the latter winding means by a first primary unilaterally conducting device.
 9. Apparatus in accordance with claim 8 wherein said means for selectively interrupting current flow comprises said second semiconductor switching means and a second primary unilaterally conducting means intercoupling the latter device and said second transformer means primary winding.
 10. Apparatus in accordance with claim 9 and further comprising a primary Zener diode connected across said second semiconductor switching means for limiting the voltage developed thereacross.
 11. Apparatus in accordance with claim 9 wherein said means for selectively establishing a current path between said first transformer means main secondary winding means and said first semiconductor switching means control electrode comprises a first unilaterally conducting device intercoupling the latter winding means and the latter control electrode.
 12. Apparatus in accordance with claim 11 wherein said means for selectively establishing a current path between said second transforming means main secondary winding means and said first semiconductor switching means control electrode comprises a second unilaterally conducting device.
 13. Apparatus in accordance with claim 12 and further comprising a Zener diode in series with said second unilaterally conducting device between the latter winding means and the latter control electrode.
 14. Apparatus in accordance with claim 13 and further comprising a primary Zener diode connected across said second semiconductor switching means for limiting the voltage developed thereacross.
 15. Apparatus for turning a semiconductor switching means on and off comprising, said semiconductor switching means having at least control and output electrodes, at least turn-on, turn-off and feedback winding means, an input terminal, means responsive to a control signal on said input terminal for producing currents in said turn-on and feedback winding means, said feedback winding means being in series with said semiconductor switching means output electrode, means responsive to the current production in said turn-on winding means for establishing a current path between said turn-on winding means and said control electrode to aid conduction of said semiconductor switching means, said turn-on and feedback winding means being poled in relationship to accelerate conduction in said semiconductor switching means, means responsive to the control signal on said input terminal for producing a current in said turn-off winding means tending to reduce the current flowing in said feedback winding means and for selectively establishing a current flow path between said turn-off winding means and said control electrode to aid nonconduction of said semiconductor switching means, said turn-off winding means and said feedback winding means being relatively poled so that reduction in current through said feedback winding means is accelerated. 